Investigation of the floor of the Black Sea, a saltwater sea connected with the Mediterranean Sea by a narrow channel...
GMAT Critical Reasoning : (CR) Questions
Investigation of the floor of the Black Sea, a saltwater sea connected with the Mediterranean Sea by a narrow channel and remote from other seas, has revealed deposits of freshwater shells dating from 5500 B.C. on an ancient shoreline. That shoreline lies 500 feet below the Black Sea's current level, and the sediment just above it contains the remains only of saltwater creatures. Scientists hypothesize that about 5500 B.C., seawater from the Mediterranean overflowed into the Black Sea basin.
Which of the following would it be most useful to ascertain in order to evaluate the scientists' hypothesis?
Passage Analysis:
| Text from Passage | Analysis |
| Investigation of the floor of the Black Sea, a saltwater sea connected with the Mediterranean Sea by a narrow channel and remote from other seas, has revealed deposits of freshwater shells dating from 5500 B.C. on an ancient shoreline. |
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| That shoreline lies 500 feet below the Black Sea's current level, and the sediment just above it contains the remains only of saltwater creatures. |
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| Scientists hypothesize that about 5500 B.C., seawater from the Mediterranean overflowed into the Black Sea basin. |
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Argument Flow:
The argument moves from presenting mysterious evidence (freshwater shells in a saltwater sea) to providing context about the location and timing, then offers a scientific explanation for this puzzle.
Main Conclusion:
Scientists believe that around 5500 B.C., Mediterranean seawater overflowed and flooded the Black Sea basin, transforming it from freshwater to saltwater.
Logical Structure:
The evidence (freshwater shells from 5500 B.C. found 500 feet below current sea level, with saltwater creature remains directly above) supports the hypothesis that a major flooding event from the Mediterranean changed the Black Sea from freshwater to saltwater around that time period.
Prethinking:
Question type:
Evaluate - We need to find information that would help us determine whether the scientists' hypothesis (Mediterranean seawater overflowed into Black Sea around 5500 B.C.) is correct or not
Precision of Claims
The hypothesis makes specific claims about timing (5500 B.C.), causation (Mediterranean overflow caused the change), and the mechanism (seawater flooding). We need to evaluate these precise elements
Strategy
For evaluate questions, we need to think of what additional information would either strengthen or weaken the scientists' hypothesis when taken to extremes. We should focus on assumptions the hypothesis relies on and what evidence could test those assumptions. The key is finding information that could swing our confidence in the hypothesis either way
This asks about the depth of the original freshwater body. While this might provide some context about the ancient environment, it doesn't help us evaluate whether the Mediterranean specifically was the source of the overflow. The depth of the original freshwater body doesn't test the key claim that Mediterranean water caused the change from freshwater to saltwater.
This compares saltwater creatures from just above the ancient shoreline to those in the topmost layers. This might tell us about changes over time in the Black Sea, but it doesn't help evaluate whether the Mediterranean was the source of the original saltwater influx. We need to know about the connection to the Mediterranean, not just internal changes within the Black Sea.
Whether freshwater shells were used as tools is completely irrelevant to evaluating the hypothesis about Mediterranean overflow. This would tell us about human activity or shell usage, but nothing about the source of the saltwater that flooded the basin.
This asks about other ancient shorelines less than 500 feet below current level. While this might provide information about sea level changes, it doesn't specifically help evaluate whether the Mediterranean was the source of the overflow. Multiple shorelines could exist regardless of what caused the initial flooding.
This directly tests the hypothesis by asking whether saltwater creatures in the sediment resemble Mediterranean creatures from the same period. This is the most useful information because if the creatures closely resemble Mediterranean species, it would strongly support the hypothesis that Mediterranean water was indeed the source. If they don't resemble Mediterranean creatures, it would weaken the hypothesis and suggest the saltwater came from elsewhere. This information directly evaluates the specific claim about Mediterranean origin.